In the field of radio communication, especially in mobile communication, a variety of information such as image and data in addition to voice is becoming transmission targets in recent years. It is anticipated that the demand for high-speed transmission becomes further increased in the future, and to perform high-speed transmission, a radio transmission technology, which utilizes limited frequency resources more effectively and achieves high transmission efficiency, has been required.
OFDM (Orthogonal Frequency Division Multiplexing) is one of radio transmission technologies, for meeting these requirements. OFDM is one of multicarrier communication technologies, whereby data is transmitted in parallel using a large number of subcarriers, and it is known that OFDM provides high frequency use efficiency and reducing inter-symbol interference under a multipath environment and is effective to improve transmission efficiency.
It is studied to perform frequency scheduling transmission and frequency diversity transmission using this OFDM on the downlink, when data for a plurality of radio communication mobile station apparatuses (hereinafter simply “mobile stations”) are frequency multiplexed on a plurality of subcarriers (see Non-Patent Document 1 for instance).
In frequency scheduling transmission, a radio communication base station apparatus (hereinafter simply “base station”) adaptively allocates subcarriers for mobile stations, based on received quality of each frequency band in each mobile station, so that it is possible to obtain a maximum multi-user diversity effect, thereby enabling extremely efficient communication. This frequency scheduling transmission scheme is mainly suitable for data transmissions when a mobile station moves at low speed. On the other hand, since frequency scheduling transmission requires feedback of received quality information from each mobile station, frequency scheduling transmission is not suitable for data transmissions when a mobile station moves at high speed. Moreover, frequency scheduling transmission is carried out based on received quality from each mobile station, and so it is difficult to apply frequency scheduling transmission to a common channel. Also, frequency scheduling is normally carried out for each subband, which groups a certain number of neighboring subcarriers into a block, and so not much frequency diversity effect is provided.
On the other hand, frequency diversity transmission maps data for the mobile stations in the subcarriers of the entire band in a distributed manner so that a high frequency diversity effect can be obtained. Moreover, frequency diversity transmission does not require feedback of received quality information from mobile stations, so that frequency diversity transmission is a useful scheme where frequency scheduling transmission is difficult to apply, as described above. On the other hand, the frequency diversity transmission is carried out regardless of received quality for each mobile station, and so multi-user diversity effect including the frequency scheduling transmission cannot be obtained.
Non-Patent Document 1: R1-050604 “Downlink Channelization and Multiplexing for EUTRA” 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun. 2005